This invention relates to a system for cooling any liquid, said cooling being performed for any purpose, including the extraction of energy from said liquid for heating purposes. More particularly, this invention is concerned with a simple and efficient system for generating and handling very cold liquids, down to and below their solid-liquid equilibrium temperature.
A cooler is a component of a liquid-chilling system in which a liquid, usually an aqueous liquid (e.g. water or brine), is cooled by a refrigerant. In a conventional system, the cooling effect comes from the evaporation of said refrigerant. The most common cooler types are: direct expansion and flooded (1990 ASHRAE Handbook: Refrigeration Systems and Applications).
In a typical direct expansion shell-and-tube cooler, the refrigerant evaporates inside tubes, while the fluid to be cooled is channeled throughout the shell by a series of baffles. In a typical flooded shell-and-tube cooler, the fluid, flowing through the tubes, gives its heat to the boiling liquid refrigerant on the shell side. These coolers are usually mounted horizontally. They are normally found in larger systems using screw or centrifugal compressors. In very large diameter shells, the heat transfer at the bottom can be adversely affected by the head of the refrigerant. This problem can be solved by spraying the liquid refrigerant all over the tubes instead of flooding them.
Freezing of the fluid can cause considerable damage to coolers therefore some freeze protection must be provided. Two methods are used. Suction pressure can be held above the one corresponding to the freezing point of the fluid; or the system can be shut down when the fluid temperature gets too close to the freezing point. For pure water, an evaporator-outlet temperature of 5.degree. C. is often considered as a safe lower limit.